Efficient and broadband metalens based coupling architecture for silicon photonics chips.

ABSTRACTWe have numerically investigated the tunable surface plasmon in graphene square-nanoring structure. Due to an enhancement of the local field, graphene surface plasmons (GSPs) can be strongly confined in the graphene grating region. The expressions of the lifetime for resonant modes have been investigated with the the finite difference time domain (FDTD) simulations and the coupled mode theory (CMT). Altering the Fermi energy and varying the carrier mobility have an important influence in optimizing the light absorption and the lifetime of GSPs. The CMT theoretical results agree well with FDTD simulations. Besides, by utilizing the different inner length and the different refractive index of substrate material, we find that the absorption peak of the GSPs structure can be tuned in a wide wavelength range. Our proposed graphene gratings structure shows good prospects in the mid-infrared region, such as ultracompact tunable integrated modulators and absorbers.

It is very useful to know the soil capabilities on different external impacts acting on it, especially for electromagnetic waves from Ground Penetrating Radar. In the underground detection domain actually, dealing with soil permittivity is one of the challenging research problems nowadays. In this paper, we study tropical soil constitution, taking in account the tropical climate region and we took Rwanda as a case study. Rwanda's elevation ranges from 1,000m (south and east) to 4,500m above sea level. The "thousand hills" terrain is dominated from north to south by a watershed (2.500m high) that separates the basin of the Congo River from that of the Nile and by the Ibirunga volcano chain. In spite of its proximity (2 degrees south) to the equator, the country enjoys a fine spring climate (due to its altitude), with two rainy seasons and two dry seasons. In fact, when considering the tropical climate region with his considerable rainfall period, it is better to collect information regarding the zone in consideration. Using Finite Difference Time Domain(FDTD) simulation with GPRMax simulator, and varying the permittivity, the aim of this paper is to have a benchmark of dry and rainfall season; this will help when doing measurements with the GPR instruments and others non destructive tools. In this paper, we analysed the clay soil (one of the component of Rwandan pedology) and from the variation of dry clay to wet clay associated with different fixed frequencies (300MHz, 600MHz, 900MHz, 1200MHz and 1500MHz). For each fixed frequency, we vary the clay permittivity from dry to wet clay and analysed data after simulation. From this benchmark, and in the near future work, we will use the GPR instrument and the Time Division Reflectometry(TDR) to verify the simulation results.

In this paper, we present finite difference time domain (FDTD) simulations of millimetre-wave propagation through the near-field plasma plume of low power Hall thrusters. The simulations are intended to address potential issues (collisions, magnetic fields) that may affect the validity of simple theory used for phase shift determination in the recent measurements of plasma density using microwave interferometry (Cappelli et al 2006 J. Phys. D: Appl. Phys. 39 4582). One-dimensional plane wave FDTD simulations indicate that plasma non-uniformities along the direction of wave propagation have only a minor effect on the phase shifts estimated from collisionless, non-magnetized wave propagation through a path-length averaged plasma slab. Three-dimensional FDTD simulations that also account for electron collisions and magnetic fields indicate that the departure from the use of usual simple models is no more than about 15%, well within the limits of uncertainty in the experimental measurements taken within the near field of these plasma sources.

New version of FDTD with GFM program in Schwarzschild space–time

ABSTRACTMicrowave sintering of ceramics in multimode cavities, particularly the use of picket-fence arrangements, has recently received considerable attention. Various types of ceramics have been successfully sintered and, in some cases, a desirable and unique “microwave effect” has been observed.At present, various aspects of the sintering process such as sample sizes and shapes, types of insulations, and the desirability of including a process stimulus such as SiC rods are considered forms of art and highly dependent on human expertise. The simulation of realistic sintering experiments in a multimode cavity may provide a better understanding of critical parameters involved and allow for the development of guidelines towards the optimization of the sintering process.In this paper, we utilize the FDTD technique to model various geometrical arrangements and material compatibility aspects in multimode microwave cavities and to simulate realistic sintering experiments. The FDTD procedure starts with the simulation of a field distribution in multimode microwave cavities that resembles a set of measured data using liquid crystal sheets. Also included in the simulation is the waveguide feed as well as a dielectric loading plate placed at the base of the cavity. The FDTD simulation thus provides realistic representation of a typical sintering experiment. Aspects that have been successfully simulated include types of insulation, role of SiC rods on the uniformity of the resulting fields, problems that may result from presence of thermocouples, and the possible shielding effects that may result from excessive use of SiC. These results as well as others showing the electromagnetic fields and power-deposition patterns in multiple ceramic samples are presented.

The numerical dispersion is one of the main factors to affect the accuracy of the finite-difference time-domain (FDTD) method. It can be easy to be taken for granted that a smaller time step leads to smaller simulation errors. This paper reveals that smaller time steps do not always make more accurate results in FDTD simulations. We analytically investigated how time steps affect the numerical dispersion of two FDTD methods: the leapfrog FDTD(2,2) method and the FDTD(2,4) method. The investigations in this paper show that in the FDTD(2,2) method, a larger time step limited by the Courant-Friedrichs-Lewy (CFL) condition is more helpful to reduce the numerical dispersion error. However, in the FDTD(2,4) method, as the time step grows, the numerical dispersion error decreases at the beginning and then increases. Several numerical examples are carried out to verify our analysis.

Plasmonics is a new and exciting field that has the potential to advance many different types of technology, from information processing and energy harvesting to sensing and imaging. The broad field of plasmonic materials and their potential to improve the functionality of cutting-edge technologies are examined in this thesis. The thesis explores the synthesis, characterization, and manipulation of plasmonic materials after providing an overview of the basic ideas behind plasmonics. Their distinct plasmonic properties and possible uses are clarified by a thorough investigation of a variety of materials, including noble metals, two-dimensional materials, metal oxides and hybrid structures. A thorough analysis of the Finite-Difference Time-Domain (FDTD) simulations used with different plasmonic materials is presented in this thesis. The theoretical foundation for FDTD simulations and their use in the investigation of plasmonic phenomena is established at the onset of the study. It then goes on to examine the properties of various plasmonic materials, such as noble metals, 2D materials and hybrid structures. The optical response, near-field enhancements, and dispersion properties of these materials are examined and contrasted using thorough simulations. This understanding of these plasmonic behaviors is utilized to control and manipulate a material’s performance and functionality in a particular technology. Using FDTD simulations, the thesis explores how material parameters, including size, shape, and dielectric constant, affect the plasmonic properties. Through the systematic variation of these parameters, valuable insights can be obtained regarding the optimization of plasmonic devices and systems' performance. The thesis also discusses new developments and avenues for future research in plasmonics, including the creation of novel materials, the investigation of hybrid plasmonic systems. It also addresses the difficulties and restrictions associated with using FDTD simulations to model plasmonic materials, including issues with accuracy and computational complexity. All things considered; this thesis offers an in-depth overview of how FDTD simulations are used to study different plasmonic materials. Through clarifying the optical characteristics, investigating dependence between parameters, and assessing new materials, it advances the field of plasmonics research and makes the creation of creative plasmonic systems and devices easier.

Tuning of InGaAsP planar photonic crystal nanocavities by local liquid crystal infiltration

We report on the fabrication of multichannel photonic crystal (PC) wavelength filters and their evaluation at wavelength division multiplexing (WDM) wavelengths. The devices utilize three-dimensional (3D) PCs consisting of Ta2O5/SiO2 multilayer thin films fabricated by the autocloning method. The 3D PCs serve as Bragg mirrors in the devices and finite-difference time-domain (FDTD) simulations of these mirrors revealed that their Bragg wavelength shifted by +19.8 nm as the in-plane lattice constant of the crystal increased from 400 nm to 800 nm. We fabricated these filters with a Ta2O5 cavity and obtained a wavelength shift of +24.0 nm.

We have proposed a three-port high efficient channel-drop filter (CDF) with a coupled cavity-based wavelength-selective reflector, which can be used in wavelength division multiplexing (WDM) optical communication systems. The coupling mode theory (CMT) is employed to drive the necessary conditions for achieving 100% drop efficiency. The finite-difference time-domain (FDTD) simulation results of proposed CDF which is implemented in two dimensional photonic crystals (2D-PC), show that the analysis is valid. In the designed CDF, the drop efficiency larger than 0.95% and the spectral line-width 0.78 nm at the center wavelength 1550 nm have been achieved.

Effects of antenna-target polarization and target-medium dielectric contrast on GPR signal from non-metal pipes using FDTD simulation

Numerical simulations have become a cornerstone technology in the development of nanophotonic devices. Specifically, 3D finite-difference time domain (FDTD) simulations are widely used due to their flexibility and powerful design capabilities. More recently, FDTD simulations in conjunction with a design methodology called inverse design has become a popular way to optimize device topology, reducing a device’s footprint and increasing performance. We implement a commercial inverse design tool to generate complex grating couplers and explore a variety of grating coupler design methodologies. We compare the conventionally designed grating couplers to those generated by the inverse design tool. Finally, we discuss the limitations of the inverse design tool and how different design strategies for grating couplers affect inverse design performance, in terms of both computational cost and performance of the resulting device.

Light-emitting diodes (LEDs) are becoming increasingly important across various sectors of the lighting industry and are being used more frequently. In the field of symbolic projection, research is increasingly focusing on implementing light modulation using energy-efficient, incoherent LEDs rather than lasers. Since light modulation in micro- and nano-optics is typically achieved through phase modulation, Finite-Difference Time-Domain (FDTD) simulations are employed for analysis. The objective of this article is to investigate different approaches for approximating incoherent monochromatic light sources within FDTD simulations. To this end, two approaches based on dipole sources are considered, as well as a method involving plane waves with modulated wavefronts based on Cosine–Fourier functions and a method based on the superposition of Gaussian beams. These methods are evaluated in terms of their accuracy using a two-dimensional double-slit configuration and are compared against a fully incoherent analytical reference.

The Finite-Difference Time-Domain (FDTD) method is used to study the scattering effects of extreme ultraviolet (EUV) mask. It requires significant amounts of memory and computation time as the fine grid size is needed for simulation. Theoretically, the accuracy can be increased as the mesh size is decreased in FDTD simulation. However, it is not easy to get the accurate simulation results for the multilayer (ML) structures by FDTD method. The transmission line theory is used to calculate the equivalent refractive index for EUV mask ML to simulate the ML as one layer of bulk artificial material. The reflectivities for EUV light with the normal incidence and small-angle oblique incidence in the bulk artificial material and EUV mask ML are simulated by FDTD method. The Fresnel's equation is used to evaluate the numerical errors for these FDTD simulations, and the results show good agreement between them. Using the equivalent refractive index material for EUV multilayer mask can reduce the computation time and have the accuracy with tolerable numerical errors. The ML structure with periodic surface roughness is also studied by this method, and it shows that only half of computation time is needed to substitute ML to a bulk equivalent refractive index material in FDTD simulations. This proposed method can accelerate the simulations of EUV mask designs.

We have simulated the distribution of electromagnetic (EM) waves through a system composed of miter bends by finite-difference time-domain (FDTD) simulation. To study the effect of mode conversion by miter bends, three shapes of miter bends have been simulated. For the miter bend that has processed grooves inside, the profile of the output EM waves is changed slightly from that of the input wave (HE11 mode). As a result, this case exhibits the best shape of the miter bend in our simulation. In the miter bend without processed grooves inside, the output EM waves change more than in the case of the miter bend with grooves, because mode conversion occurs at the surface in miter bends without grooves. In the simple bend, which changes the direction of EM waves gradually, the profile of the output EM waves is deformed and the input profile is not conserved. Comparing the above three cases, we found that the grooves lead to more efficient to conservation of the profile of EM waves.